1. Field of the Invention
The present invention relates in general to displays. More particularly, the present invention relates to electrophoretic displays.
2. Description of Related Art
Proliferation of computers, and other electronic devices, such as for example advanced wireless telephones, personal digital assistants (PDA), electronic games, and new types of television monitors have increased the importance of display technologies.
Cathode Ray Tubes (CRT) and Liquid Crystal Displays (LCD) are the two most common types of displays. CRT displays are presently dominant. LCD displays have the advantage that they are essentially ‘flat’, having a small depth compared to the dimensions of the viewable area. The flatness of LCD displays compared to traditional CRT displays makes them especially suitable for use in small size portable devices, such as notebook computers, PDAs, and wireless telephones, and is also attractive for larger home entertainment, and commercial displays.
Flatness is a generally regarded as a positive attribute in display technology, and there are other types of displays, aside from LCD displays, that are flat. One other type of flat display technology is electrophoretic. Electrophoretic displays comprise a suspension of particles in a liquid. The suspension is held between two flat walls, one of which is transparent and serves as a viewable display surface. Optionally the suspension is encapsulated in many small capsules that are held between the two flat walls, or emulsified in a polymeric matrix. The particles have optical properties that are different from the liquid in which they are suspended. For example electrophoretic displays in which the particles are more reflective of light than the liquid have been proposed and electrophoretic displays in which the particles are luminescent have also been proposed. Each type is suited to use under particular ambient light conditions. Due to the electrochemical properties of the particles, and of the liquid, the particles spontaneously acquire a net charge when placed in the liquid. Having a charge, the particles can be caused to translate by an externally applied electric field. Electrodes are provided for imagewise application of electric fields to the suspension. Selectively causing the particles to translate to the viewable display surface, according to an image pattern, causes an image to appear at the viewable display surface. In as much as electrophoretic displays work by application of electric fields, they are potentially very efficient in terms of current consumption, which is a significant attribute for battery operated portable electronic devices.
Certain display applications, such as portable electronic devices, typically require that a display be able to operate in a wide range of ambient light conditions, i.e., in conditions ranging from mid day sun, to complete darkness.
It would be desirable to have an electrophoretic display that is capable of operating in wide range of ambient light conditions.